Then, you need to press the "Convert file" button and browse to the CSV (or other) file that contains your coordinates. Choose the appropriate number of header lines (the non-data lines you want to ignore) and select the fields for the easting and northing etc.
Finally, press the "Convert" button and select an output file type from the file type drop-down list. e.g. CSV or KML.
If you want to send the output to a KML file, then the "to" coordinate system must be "Longitude/Latitude WGS84".